Activating molybdenum carbide via a surface sulfur modification to enhance hydrogen evolution activity

Molybdenum carbide (Mo2C) was regarded as one of the most promising catalysts for hydrogen evolution reaction (HER) due to its Pt-like electronic structure. In practice, however, the catalytic performance of Mo2C is always hampered by the inevitable oxidation on its surface. Herein, we developed a simple and efficient strategy to improve the HER activity of Mo2C using sulfur as a "modifier", in which sulfur atoms were used to replace a portion of the oxygen atoms in the surface oxide layer to activate the surface. The experimental results demonstrated that a moderate sulfur modification could significantly improve the HER performance. Theoretical studies further revealed that the strong hydrogen bonding of Mo atoms in the oxide layer is the primary reason that impairs HER performance, whereas the S modification can shift down the D-band center of Mo, effectively weakening the Mo-H bond. As expected, the S-modified Mo2C exhibited superior performance, affording a low overpotential of 117 mV at 10 mA cm-2 for catalyzing the HER in 0.5 M H2SO4. This work provides a convenient and effective way for the development of transition metal carbide catalysts. (c) 2022 Elsevier B.V. All rights reserved.